A comparison of the Slaughter skinfold-thickness equations and BMI in predicting body fatness and cardiovascular disease risk factor levels in children

Abstract

Background: Although estimation of percentage body fat with the Slaughter skinfold-thickness equations (PBF(Slaughter)) is widely used, the accuracy of this method has not been well studied.

Objective: The objective was to determine the accuracy of the Slaughter skinfold-thickness equations.

Design: We compared agreement between PBF(Slaughter) and estimations derived from dual-energy X-ray absorptiometry (PBF(DXA)) in 1169 children in the Pediatric Rosetta Body Composition Project and the relation to cardiovascular disease risk factors, as compared with body mass index (BMI), in 6725 children in the Bogalusa Heart Study.

Results: PBF(Slaughter) was highly correlated (r = 0.90) with PBF(DXA), but it markedly overestimated levels of PBF(DXA) in children with large skinfold thicknesses. In the 65 boys with a sum of skinfold thicknesses (subscapular- plus triceps-skinfold thicknesses) ≥ 50 mm, PBF(Slaughter) overestimated PBF(DXA) by 12 percentage points. The comparable overestimation in girls with a high skinfold sum was 6 percentage points. We also found that, after adjustment for sex and age, BMI showed slightly stronger associations with lipid, lipoprotein, insulin, and blood pressure values than did PBF(Slaughter).

Conclusions: These results indicate that PBF(Slaughter), which was developed among a group of much thinner children and adolescents, is fairly accurate among nonobese children, but markedly overestimates the body fatness of children who have thick skinfold thicknesses. Furthermore, PBF(Slaughter) has no advantage over sex- and age-adjusted BMIs at identifying children who are at increased risk of cardiovascular disease based on lipid, lipoprotein, insulin, and blood pressure values.

FIGURE 1.

Values are based on the 626 boys and 570 girls in the Pediatric Rosetta Body Composition Project. A: Relation of DXA-determined PBF (PBF_DXA) with PBF calculated from the Slaughter equations (PBF_Slaughter). Data points represent the individual children, the dashed line is the line of identity (PBF_DXA = PBF_Slaughter), and the solid line is the smoothed (Lowess) curve. B: Bland-Altman plot for the agreement between PBF_DXA and PBF_Slaughter. Data points represent the individual children, and the black line is the Lowess curve. Overall medians are represented by the large diamonds, and the dashed lines represent the 95% CIs for the agreement between the 2 methods. C: Relation of SF sum to percentage body fat. Based on the Slaughter equations, all estimates of PBF for children with an SF sum ≥35 mm would fall on straight lines, with slopes of 0.783 (boys) and 0.546 (girls). The data points represent the DXA-calculated body fatness of each child, and the dashed lines represent the Lowess-estimated association between SF sum and PBF_DXA. Among boys, the discrepancies between PBF_DXA and PBF_Slaughter increase substantially at higher SF sum levels. The large circle represents a boy with an SF sum of 84 mm (first row of Table 3). DXA, dual-energy X-ray absorptiometry; Lowess, locally weighted scatter plot smoothing; PBF, percentage body fat; PBF_DXA, percentage body fat estimated by using dual-energy X-ray absorptiometry; PBF_Slaughter, percentage body fat estimated by using the Slaughter skinfold-thickness equations; SF sum, sum of subscapular and triceps skinfold thicknesses.